This section of the report will provide a rolling three month update on a monthly basis of the state of the climatic and ecological indicators used in monitoring areas at risk to RVF activity. These indicators include, global SST anomalies patterns, Equatorial Western Indian Ocean (WIO) and Eastern Pacific Ocean (EPO: NINO 3.4) SST anomalies, Southern Oscillation Index (SOI) and Outgoing Longwave Radiation (OLR) anomalies, Rainfall and anomalies, Normalized Difference Vegetation index anomalies and RVF risk map for Africa and the Arabian Peninsula.
1. SOI and SST Indices
The SOI index value dropped to -0.1 in October from 0.3 in September, this fluctuation is within the normal range of values that characterize neutral ENSO conditions. This is a pattern that continues to be exhibited by the SOI since the beginning of the year. Correspondingly, October monthly SST anomalies in the NINO3.4 SST region are also near-normal with a value of -0.33°C and so are the WIO SST (-0.35°C) anomalies indicating a moderate cooling over this basin in the last three months. At the moment, all the atmospheric and oceanic indicators are in convergence with persistence of ENSO- neutral conditions. The latest statistical and coupled model forecasts continue to indicate that ENSO-neutral (Niño-3.4 index between -0.5°C and 0.5°C) will persist into the Northern Hemisphere spring 2014.
Cumulative NDVI anomalies for Africa for August - October 2013 show band of positive anomalies across the Sahel region in response to the above normal rainfall from over the last 2-3 months. The RVF risk map below was derived from thresholding NDVI anomaly data to detect areas persistent of above normal NDVI. Periods of widespread and prolonged heavy rainfall lead to flooding of dambos and anomalous green up in vegetation, creating ideal ecological conditions for the emergence RVF vectors. For the period August - October 2013, the RVF persistence model continues to identify isolated areas in South Sudan, Niger, Mali, southern Mauritania and Chad where ecological conditions would support the emergence of RVF vectors. These should be the regions of focus at this time given the above-normal rainfall and NDVI conditions and, the recently reported RVF activity in Mauritania and Senegal.